I really don't want to get into an argument where I'm defending what might turn out to be another excuse.... But you do know power outages aren't generally global right? His neighborhood might be down, but the area where the mast is might be fine, or the area where he works, or the area where his parents live.... you get the idea? Mobile phones are mobile and so are people to a certain extent.
Zip has an established record of "failing" deadlines, there is a good chance this is no different, there is also a chance that this is a legitimate excuse.... either way only time will tell.